How to select all objects of a certain viewport draw type in blender 2.8?
Quick little script

The following script changes all objects in the context scene  displayed as bounds to wire.

import bpy
context = bpy.context
scene = context.scene
bounds = [o for o in scene.objects if o.display_type == 'BOUNDS']

for o in bounds:
    o.display_type = 'WIRE'


It is often more useful to use the selection, replace scene.objects with context.selected_objects to only change only those in selection that match the criteria.